Co-initiated polyether polyol and process for its preparation

ABSTRACT

Process for the preparation of a co-initiated polyether polyol, which process comprises the steps of (a) preparing a mixture of at least one aromatic initiator, at least one polyethylene glycol and optionally one or more aliphatic initiators, (b) reacting the mixture obtained in step (a) in the presence of a suitable alkoxylation catalyst with at least one alkylene oxide having three or more carbon atoms per molecule using such quantity of alkylene oxide that the polyether polyol obtained has a hydroxyl value in the range of from 150 to 400 mg KOH/g, and (c) recovering the co-initiated polyether polyol. The co-initiated polyether polyol is very suitable for (the preparation of rigid polyisocyanurate-modified polyurethane foams. Such foams have a good flame retardancy.

[0001] The present invention relates to a co-initiated polyether polyol,to a process for the preparation of such polyether polyol, to polyolformulations containing such polyether polyol and topolyisocyanurate-modified polyurethane foams obtained from saidpolyether polyol.

[0002] Nowadays polyisocyanurate-modified rigid polyurethane foams(PIR/PUR foams) become more and more accepted in the building insulationmarket, anyhow in Europe. In this particular market PIR/PUR foams haveto compete with the conventional rigid polyurethane foams (PUR foams).In terms of foam properties PIR/PUR foams are very similar to PUR foams.The formulation characteristics of both foams are, however, different.The main difference concerns the amount of isocyanate used to preparethe foam: this amount is higher for PIR/PUR foams. Accordingly, theisocyanate index for PIR/PUR foams is higher than that for PUR foams.The relatively large excess of isocyanate groups in PIR/PUR foamingformulations is reacted by adding trimerisation catalyst(s) to thereaction mixture. In this way the isocyanurate structures are formed.These isocyanurate structures improve the fire retardancy and thermalstability of the final foam and also induce an increased friability.

[0003] At present difunctional aromatic polyester polyols are commonlyused in the manufacture of PIR/PUR foams. One category of such polyesterpolyols typically used are the polyester polyols produced from phthalicanhydride and diethylene glycol. Another category uses either the heavyresidue of the production of dimethyl terephthalate or scraps ofrecycled polyethylene terephthalate (PET) as the feedstock.

[0004] The present invention aims to provide a dedicated polyetherpolyol, which can be used for producing PIR/PUR foams without using anypolyester polyol. A further purpose of the present invention is toprovide a method for producing such dedicated polyether polyol. Still afurther object is to provide a PIR/PUR foam, of which the polyolcomponent is entirely polyether polyol based and of which theend-properties are at least comparable to those of the conventionalpolyester polyol-based PIR/PUR foams.

[0005] The term “polyether polyol” as used in this connection refers topolyols comprising poly(alkylene oxide) chains, which polyols arenormally obtained by reacting a polyhydroxy initiator compound with atleast one alkylene oxide and optionally other compounds. The term“co-initiated polyether polyol” refers to a polyether polyol obtained bythe alkoxylation of a blend of at least two different polyhydroxycompounds. The term “molecular weight” as used throughout thisspecification refers to number average molecular weight. The term“average molecular weight” refers to number average molecular weight permole of initiator used.

[0006] The above objects have been realised by a specific co-initiatedpolyether polyol based on an aromatic initiator, polyethylene glycol,optionally an aliphatic initiator and alkylene oxide.

[0007] Accordingly, in a first aspect the present invention relates to aprocess for the preparation of a co-initiated polyether polyol, whichprocess comprises the steps of:

[0008] (a) preparing a mixture of:

[0009] (a1) at least one aromatic initiator containing at least twoactive hydrogen atoms per molecule and

[0010] (a2) at least one polyethylene glycol having a molecular weightin the range of from 400 to 1000 and

[0011] (a3) optionally one or more aliphatic initiators containing from2 to 6 active hydrogen atoms per molecule in an amount of at most 20mole % based on total moles of (a1) and (a3), wherein the molar ratio of(a1) to (a2) is in the range of from 0.5:1 to 5:1, and

[0012] (b) reacting the mixture obtained in step (a) in the presence ofa suitable alkoxylation catalyst with at least one alkylene oxide havingthree or more carbon atoms per molecule using such quantity of alkyleneoxide that the polyether polyol obtained has a hydroxyl value in therange of from 150 to 400 mg KOH/g, and

[0013] (c) recovering the co-initiated polyether polyol.

[0014] The aromatic initiator used as component (a1) in step (a) may beany aromatic initiator known in the art to be suitable for acting as astarter molecule in the preparation of polyether polyols. Suitablearomatic initiators should contain at least two active hydrogen atomsper molecule available for reaction with alkylene oxide. Such activehydrogen atoms are typically present in the form of hydroxyl groups, butmay also be present in the form of e.g. amine groups. Preferredinitiators are those aromatic initiators containing from 2 to 5, morepreferably 2 or 3 and most preferably 2 active hydrogen atoms in theform of hydroxyl groups per molecule. Concrete examples of suitablearomatic initiators include 2,2′-bis(4-hydroxylphenyl)propane (bisphenolA), 2,2′-bis(4-hydroxylphenyl)butane (bisphenol B) and2,2′-bis(4-hydroxylphenyl)methane (bisphenol F). Similar compounds,wherein the hydroxyphenyl moiety contains one or more alkylsubstituents, preferably methyl, may also be used. Bisphenol A is apreferred aromatic initiator.

[0015] The aromatic initiator component (a1) may consist of one solearomatic initiator or of a blend of two or more different aromaticinitiators provided such blend contains on average at least two activehydrogen atoms per initiator molecule. The aromatic initiator component(a1) may also be used in combination with an aliphatic initiatorcomponent (a3) consisting of one or more aliphatic initiators containingfrom 2 to 6 active hydrogen atoms per molecule. Such aliphatic initiatorcomponent, if present, is used in an amount of at most 20 mole % basedon total moles of (a1) and (a3), preferably from 0.5 to 10 mole %. Theaverage number of active hydrogen atoms per initiator molecule in such acombination should preferably be in the range of from 2 to 4, morepreferably from 2 to 3 and most preferably equals 2. It will beunderstood that the nominal average functionality of the resultingpolyether polyol will correspond with the number of active hydrogenatoms per initiator molecule. Examples of suitable aliphatic initiatorsare those known in the art including diethylene glycol, glycerol,pentaerythritol tri-methylolpropane, triethanolamine, mannitol andsorbitol. It has, however, been found particularly advantageous to useno aliphatic initiator component, inter alia because it adds to the costof the formulation while having no recognisably beneficial effect on theend-properties of the PIR/PUR foam eventually obtained.

[0016] Suitable polyethylene glycols to be used as component (a2) arethose polyethylene glycols having a molecular weight in the range offrom 400 to 1000, preferably from 400 to 800, more preferably from 450to 700. It will be understood that polyethylene glycols contain twohydroxyl groups, which are available to react with alkylene oxide. Thepolyethylene glycol component (a2) may consist of one or more,preferably one or two, polyethylene glycols. If more than onepolyethylene glycol is used, they should all meet the above requirementas to molecular weight. Suitable polyethylene glycols are commerciallyavailable from several suppliers or can be prepared by methods known inthe art.

[0017] In the process of the present invention it is essential that thearomatic initiator component (a1) and the polyethylene glycol component(a2) are admixed before alkylene oxide is allowed to react with theactive hydrogen atoms present in both polyethylene glycol and initiatorcompound(s). The components (a1) and (a2) are mixed in a molar ratio of(a1) to (a2) in the range of from 0.5:1 to 5:1, preferably 1:1 to 4:1,more preferably 1:1 to 3:1. It is preferred that one aromatic initiatoris mixed with one polyethylene glycol in step (a) in a molar ratio ofaromatic initiator to polyethylene glycol of from 1:1 to 4:1. If anyaliphatic initiator component (a3) is present this component should alsohe admixed with components (a1) and (a2) prior to the reaction withalkylene oxide. By first mixing the initiator(s) and polyethyleneglycol(s) before reaction with alkylene oxide, it is ensured that aco-initiated polyether polyol is obtained containing both aromaticmoieties (originating from the aromatic initiator) and ethylene oxidemoieties (originating from the polyethylene glycol). It was found thatsuch composition of the co-initiated polyether polyol is very beneficialfor the fire retardant properties of the PIR/PUR foam eventuallyobtained therefrom.

[0018] After initiator(s) and polyethylene glycol(s) have been mixed instep (a) the resulting mixture is reacted with at least one alkyleneoxide having three or more carbon atoms per molecule using such quantityof alkylene oxide that the polyether polyol obtained has a hydroxylvalue in the range of from 150 to 400 mg KOH/g, preferably from 175 to350 mg KOH/g and more preferably 200 to 300 mg KOH/g. Most preferably,the OH value is at most 300 mg KOH/g. Such OH values will normally beobtained when per mole of aromatic initiator component from 1.2 to 10moles of alkylene oxide are used, more particularly from 2 to 8 moles.

[0019] The alkylene oxide(s) used should contain at least three carbonatoms per molecule. Suitable alkylene oxides, then, include inparticular propylene oxide and butylene oxide, although higher alkyleneoxides may also be applied. Most advantageously, however, propyleneoxide is used as the sole alkylene oxide.

[0020] Step (a) of the process according to the present invention ispreferably carried out at such temperature and pressure that theresulting mixture is a homogeneous liquid. Suitably, the temperatureapplied may vary from 10 to 175° C., preferably from 25 to 150° C., morepreferably from 75 to 140° C., and the pressure from 0.5 to 10 bara,although it is preferred to work at a pressure of 1 to 2 bara. Thecomponents are suitably mixed by dissolving the aromatic initiatorcomponent, optionally together with the aliphatic initiator component,in the polyethylene glycol component. Step (b) of the present process iscarried out under conditions normally applied in the alkoxylation ofpolyhydroxyl compounds. Accordingly, temperatures applied are suitablyin the range of from 50 to 150° C., preferably 80 to 140° C., andpressures applied from 0.5 to 10 bara with atmospheric pressure beingparticularly preferred.

[0021] The alkoxylation is typically carried out in the presence of asuitable alkoxylation catalyst as is well known in the art. Both acidand basic catalysts can be used. Examples of acid catalysts includeLewis acids like boron trifluoride, stannic chloride or combinations offerric chloride with thionyl chloride. Double metal cyanide catalysts,often comprising zinc hexacyano cobaltate as the active ingredient, mayalso be used. For the purpose of the present invention, however, it ispreferred to use basic catalysts. The basic catalyst most commonly usedis potassium hydroxide. The catalyst is suitably added to the reactorafter when all initiator is present in the reactor, but before thealkylene oxide is added. The amount of catalyst used is in the rangenormally applied, i.e. from 0.05 to 2 wt % based on final product. Afterthe alkoxylation the catalyst is suitably removed by neutralization witha suitable neutralizing agent, such as acetic acid, phosphoric acid ordisodium dihydrogen pyrophosphate.

[0022] The polyether polyol can be recovered by the measuresconventionally applied. Such measures will typically include one or moreof the following treatments: neutralization (to remove the catalyst),dewatering, steam stripping and drying and filtration.

[0023] In a further aspect the present invention relates to aco-initiated polyether polyol having an aromaticity in the range of from5 to 35 wt % and an average molecular weight in the range of from 300 to1000, which polyether polyol is obtainable by a process as describedabove.

[0024] In this specification the term “aromaticity” refers to the weightpercentage of aromatic carbon atoms, i.e. carbon atoms contained in anaromatic ring structure, present in the co-initiated polyether polyolrelative to the total weight of the co-initiated polyether polyol. Theco-initiated polyether polyol according to the present invention has anaromaticity in the range of from 5 to 35 wt %, preferably 10 to 30 wt %,more preferably 15 to 25 wt %.

[0025] The co-initiated polyether polyol according to the presentinvention furthermore has an average molecular weight in the range offrom 300 to 1000, with an average molecular weight of from 350 to 800,more in particular 400 to 600, being preferred. The nominal averagefunctionality of the polyether polyol will normally be in the range offrom 2 to 6. However, it has been found particularly advantageous thatthe co-initiated polyether polyol has a nominal average functionality inthe range of from 2 to 4, more preferably 2 to 3 and most preferably of2.

[0026] The hydroxyl value of the co-initiated polyether polyol is in therange of from 150 to 400 mg KOH/g, preferably from 175 to 350 mg KOH/gand more preferably 200 to 300 mg KOH/g. Most preferably, the OH valueis at most 280 mg KOH/g. The ethylene oxide content of the polyetherpolyol depends on the amount and molecular weight of the polyethyleneglycol(s) used in its preparation. Suitably, the ethylene oxide contentwill be in the range of from 20 to 60 wt %, with 30 to 50 wt % beingpreferred.

[0027] In a still further aspect the present invention relates to apolyether polyol formulation comprising a co-initiated polyether polyolas defined above in admixture with a rigid, aromatic polyether polyolhaving a hydroxyl value of at least 400 mg KOH/g, preferably of from 500to 600, and an average nominal functionality of at least 2.3, preferablyof from 3 to 4.5.

[0028] The rigid, aromatic polyether polyol may be any such polyol knownin the art which meets the above requirements as to hydroxyl value andaverage nominal functionality. These polyols are well known andcommercially available from several suppliers.

[0029] The present invention also relates to a process for thepreparation of a rigid polyisocyanurate-containing polyurethane foam(PIR/PUR foam), which process comprises foaming a formulation comprising

[0030] (a) a co-initiated polyether polyol or a polyether polyolformulation as described herein before,

[0031] (b) a polyisocyanate in such amount that the isocyanate index isat least 150, preferably from 180 to 600,

[0032] (c) polyurethane catalyst and/or polyisocyanurate catalyst,

[0033] (d) one or more blowing agents, and

[0034] (e) usual auxiliaries.

[0035] The polyisocyanate, used as component (b), may be anypolyisocyanate known to be suitable in rigid polyurethane foams.Suitably, aromatic polyisocyanates are used and any di-, tri-, tetra-and higher functional aromatic polyisocyanate may be used. InEP-A-0,778,302, for instance, a list with suitable polyisocyanates isgiven. Preferred polyisocyanates are 2,4- and 2,6-toluene diisocyanateas well as mixtures thereof; 4,4′-diphenyl-methane diisocyanate (MDI);polymethylene polyphenylene polyisocyanate and polymeric MDI, a mixtureof polyisocyanates with MDI as the main component.

[0036] The polyisocyanate is used in such quantity that the isocyanateindex is at least 150, preferably-from 180 to 600, more preferably from200 to 400 and most preferably from 200 to 320. As is well known in theart, the isocyanate index is defined as the 100 times the equivalenceratio of isocyanate groups to active hydrogen atoms, such as thosepresent in the polyol component (a) and water

[0037] The polyurethane catalyst, that may be employed as (part of)component (c) can be any urethane catalyst known to be suitable inurethane production. Suitable catalysts are those described in e.g.EP-A-0,358,282 and U.S. Pat. No. 5,011,908 and include tertiary amines,salts of carboxylic acids and organometallic catalysts. Examples ofsuitable tertiary amines are triethylene diamine, N,N-dimethylcyclohexyl amine, N-methyl morpholine, diethyl ethanol amine, diethanolamine, dimethyl benzyl amine and dimethyl cyclohexyl amine. Suitableorganometallic catalysts include stannous octoate, stannous oleate,stannous acetate, stannous laureate, lead octoate, nickel naphthenateand dibutyltin dichloride. Further examples of organometallic catalystsare described in U.S. Pat. No. 2,846,408. Of course, mixtures of two ormore of the aforementioned catalysts may also be used. Suitablepolyisocyanurate catalysts or trimerisation catalysts are also wellknown in the art and include sodium acetate, potassium octoate orpotassium acetate, e.g. dissolved in diethylene glycol, and strong basicmaterials, such as quaternary ammonium salts andtris(dimethylaminopropyl)triazine.

[0038] The amounts of polyisocyanurate catalyst and polyurethanecatalyst will usually be in the range of from 1.0 to 8.0 parts by weight(pbw), more suitably 2.0 to 5.0 pbw, per 100 pbw of polyether polyol.

[0039] Suitable blowing agents are those conventionally applied in rigidpolyurethane production and include water, partly halogenated alkanes,aliphatic alkanes and alicyclic alkanes. Fully halogenated hydrocarbonsmay also be used, but are less preferred due to their ozone depletingeffect. Concrete examples of suitable blowing agents then include water,1-chloro-1,1-difluoroethane, cyclopentane, cyclohexane, n-pentane,isopentane and mixtures of two or more of these. A combination of wateron the one hand and n-pentane or cyclopentane on the other hand has beenfound particularly useful. The amount of blowing agent used may rangefrom 0.1 to 5 pbw per 100 pbw of polyol for water and 0.1 to 20 pbw per100 pbw of polyol in case of partly halogenated hydrocarbons, aliphaticalkanes and alicyclic alkanes.

[0040] The auxiliaries, which form component (e), are the usualcomponents and may include foam stabilisers, flame retardants, colouringagents and fillers. For instance, organosilicone surfactants are oftenused as foam stabilisers.

[0041] The present invention, finally, also relates to a rigid PIR/PURfoam obtainable by the process as described above, i.e. by foaming aformulation comprising the components (a) to (e) as defined hereinbefore.

[0042] The PIR/PUR foam according to the invention typically has a freerise density of 10 to 100 kg/m³, suitably 20 to 60 kg/m³, and acompressive strength in the direction of the free rise of at least 140kPa, preferably of 150 to 200 kPa, which is very good. Its flameretardant properties are also excellent: it meets the DIN4102 B2 smallscale fire test.

[0043] The invention is further illustrated with the following exampleswithout limiting the scope of the invention to these particularembodiments

EXAMPLE 1

[0044] Preparation of Polyether Polyol

[0045] A solution of bisphenol A in polyethylene glycol was reacted withpropylene oxide (molar ratio bisphenol A: polyethylene glycol:propyleneoxide is 2.0:1.0:6.5) as follows.

[0046] Polyethylene glycol having a molecular weight of 600 was added toa reactor and the reactor was heated to 100° C. Then, bisphenol A wasadded under continuous stirring and the temperature was raised to 120°C. After the bisphenol A had dissolved in the polyethylene glycol 0.15wt % on final product of potassium hydroxide (KOH) was added as asolution in water to the solution. The water present in the KOH solutionwas removed by keeping the reactor at 120° C. and applying a vacuum ofbetween 7 and 13 mbara until the water content had reduced to less than0.5 wt % on total reaction mixture. Propylene oxide was then added at110° C., in such manner that the pressure in the reactor remained below5 bar. The alkoxylation reaction was allowed to proceed until thepressure had reached a constant value of 1.5 bara. The KOH catalyst wasremoved by neutralising the reaction mixture with acetic acid.

[0047] The resulting co-initiated polyol product had an aromaticity of20.1 wt %, an OH-value of 235 mg KOH/g, a propylene oxide content of 26wt %, an ethylene oxide content of 42 wt % and an average molecularweight of 477.

EXAMPLE 2

[0048] Preparation of PIR/PUR Foam

[0049] The polyether polyol prepared in Example 1 was used in a foamformulation consisting of: 50 pbw Rigid polyol A 50 pbw co-initiatedpolyether polyol of Example 1 20 pbw Amgard dimethyl methyl phosphonateex Albright & Wilson 1.5 pbw DABCO DC193, a silicone surfactant ex AirProducts 2.65 pbw Jeffcat TR, a trimerisation catalyst ex HuntsmanChemicals 1.52 pbw water 14.2 pbw n-pentane 227.3 pbw CARADATE 30, apolymeric MDI ex Shell.

[0050] (Amgard, DABCO, Jeffcat and CARADATE are trade marks).

[0051] Polyol A was a diethanol amine/aromatic propylene oxide-basedpolyol having a hydroxyl value of 530 mg KOH/g polyol and a nominalaverage functionality of 3.0 eq/mole.

[0052] The isocyanate index of this system was 200.

[0053] The foam was prepared by making a preblend of all components butthe polyisocyanate. Subsequently, the polyisocyanate was poured into thepreblend and the reaction mixture was stirred for 10 seconds and thenpoured into a polyethylene bag. Thus, a free-rise PIR/PUR foam wasformed.

[0054] The properties of the PIR/PUR foam are listed in Table I.

EXAMPLE 3

[0055] Preparation of PIR/PUR Foam

[0056] The polyether polyol prepared in Example 1 was used in a foamformulation consisting of: 100 pbw co-initiated polyether polyol ofExample 1 20 pbw Amgard dimethyl methyl phosphonate 3.0 pbw DABCO K15, atrimerisation catalyst ex Air Products 1.5 pbw DABCO DC193 1.0 pbw water16.0 pbw n-pentane 212.4 pbw CARADATE 30.

[0057] The isocyanate index of this system was 300.

[0058] A free-rise PIR/PUR foam was prepared in the same manner as inExample 2.

[0059] The properties of the PIR/PUR foam are listed in Table I. TABLE IProperties of PIR/PUR foams Example 2 Example 3 Isocyanate index 200 300Free rise density (kg/m³) 28.4 30.0 Compressive strength (kPa) 139 161Closed cell content (% v/v) * 83.9 82.9 Maximum flame height (cm) **15.0 11.0

1. Process for the preparation of a co-initiated polyether polyol, whichprocess comprises the steps of: (a) preparing a mixture of: (a1) atleast one aromatic initiator containing at least two active hydrogenatoms per molecule and (a2) at least one polyethylene glycol having amolecular weight in the range of from 400 to 1000 and (a3) optionallyone or more aliphatic initiators containing from 2 to 6 active hydrogenatoms per molecule in an amount of at most 20 mole % based on totalmoles of (a1) and (a3), wherein the molar ratio of (a1) to (a2) is inthe range of from 0.5:1 to 5:1, (b) reacting the mixture obtained instep (a) in the presence of a suitable alkoxylation catalyst with atleast one alkylene oxide having three or more carbon atoms per moleculeusing such quantity of alkylene oxide that the polyether polyol obtainedhas a hydroxyl value in the range of from 150 to 400 mg KOH/g, and (c)recovering the co-initiated polyether polyol.
 2. Process according toclaim 1, wherein one aromatic initiator is mixed with one polyethyleneglycol in step (a) in a molar ratio of aromatic initiator (a1) topolyethylene glycol (a2) of from 1:1 to 4:1.
 3. Process according toclaim 2, wherein the aromatic initiator is bisphenol A.
 4. Processaccording to any one of claims 1-3, wherein such quantity of alkyleneoxide is used in step (b) that the polyether polyol obtained has ahydroxyl value in the range of from 200 to
 300. 5. Process according toany one of claims 1-4, wherein the sole alkylene oxide used in step (b)is propylene oxide.
 6. Co-initiated polyether polyol having anaromaticity in the range of from 5 to 35 wt % and an average molecularweight in the range of from 300 to 1000, which polyether polyol isobtainable by a process as claimed in any one of claims 1-5. 7.Co-initiated polyether polyol according to claim 6 having an ethyleneoxide content in the range of from 20 to 60 wt %, preferably 30 to 50 wt%.
 8. Polyether polyol formulation comprising a co-initiated polyetherpolyol as claimed in claim 6 or 7 in admixture with a rigid, aromaticpolyether polyol having a hydroxyl value of at least 400 mg KOH/g,preferably of from 500 to 600, and an average nominal functionality ofat least
 3. 9. Process for the preparation of a rigidpolyisocyanurate-containing polyurethane foam, which process comprisesfoaming a formulation comprising (a) a co-initiated polyether polyol asclaimed in claim 6 or 7 or a polyether polyol formulation as claimed inclaim 8, (b) a polyisocyanate in such amount that the isocyanate indexis at least 150, preferably from 180 to 600, (c) polyurethane catalystand/or polyisocyanurate catalyst, (d) one or more blowing agents, and(e) usual auxiliaries.
 10. Rigid polyisocyanurate-containingpolyurethane foam obtainable by the process according to claim 9.